As September ended, it seemed like a lock that the Atlantic hurricane season would run out of storm names for the only the third time in its history. But since Oct. 6, storm activity has shut down with not a single named system since.

With just over a month left in hurricane season, it’s rather unclear whether the list of names will finally be exhausted for a second straight year.

The nor’easter currently lashing the Northeast United States is a possible candidate to become Wanda, the 21st and final name on 2021′s list. The National Hurricane Center says it has a 40 percent chance of transforming into a tropical or subtropical entity as it interacts with the warm waters of the Gulf Stream.

Even if the nor’easter isn’t named, there’s still a chance that a tropical storm or hurricane forms in November which, on average, produces one named storm.

Whether Wanda forms will determine if 2020 and 2021 make history as the first back-to-back years to exhaust the list of Atlantic storm names. 2021 would also become only the third year on record to do so.

A brief history of named storms

To understand how we got here, it’s helpful to understand how storms are named.

The Hurricane Center assigns names alphabetically to tropical systems as soon as their wind speed increases beyond the 39 mph threshold necessary to become a tropical storm. This means the first storm of the year is named with an A, the second named with a B, etc. On average, there are approximately 14 such named storms a year, so the Hurricane Center only has to use letters “A” through “N” during a normal season.

The World Meteorological Organization maintains six alphabetic lists of 21 names that rotate through a six-year cycle. Names are not assigned to the letters Q, U, X, Y and Z due to the paucity of choices. Storms that are harmful to life and property are retired from the list and replaced.

Through the early 2000s, the lists of 21 names were sufficient to capture the observed number of storms. Only twice, in 1969 and 1995, were there more than 15 named storms; neither season reached 20.

But in 2005, an astonishing 27 tropical storms and hurricanes formed, blowing through the conventional name list. After Wilma became the season’s 21st storm in October of that year, it became clear that a supplemental list of names was necessary. It was agreed upon that the Greek alphabet would supply auxiliary names. On Oct. 22, 2005, the Hurricane Center declared that Tropical Storm Alpha had formed.

A season so extraordinarily active would not remain in lone company for long, though. 2020 managed to top 1995′s count of 27 named storms, with a 30-storm run that made it as far into the Greek alphabet as Iota.

The 2020 hurricane season, however, showed why naming storms after Greek letters was problematic. What if you had to retire a Greek-letter-named storm? Eta and Zeta, which ravaged Nicaragua and Louisiana, both merited replacement under World Meteorological Organization policy.

Responding to this concern, the World Meteorological Organization decided it would stop using Greek letters if the conventional list of 21 names was exhausted. Instead, starting this year, it has developed a new supplementary name list. Storms on this additional list can be retired and replaced if they result in devastation.

2021’s race to 21-named storms

Through the end of September, the Atlantic was actually ahead of 2005’s pace in working through the list of names. But it has since fallen into third place.

There are several atmospheric factors contributing to a season that has already secured a bronze medal for named storm occurrence. A multiyear climate oscillation known as La Niña is showering the basin with conditions supportive for tropical cyclone development, and global warming is almost certainly increasing the oceanic heat content that storms use to form and strengthen.

However, just because 2021 may become only the third season to overshoot the naming list does not mean this is the third most supportive hurricane environment in known meteorological history. Nonatmospheric factors probably also play a role.

Brian McNoldy, senior research associate at the University of Miami and hurricane expert for Capital Weather Gang, notes that a significant factor driving the increase in named storm occurrence could be improvements in weather satellite technology.

“Satellites have evolved and improved drastically over the past 55 years or so since they started providing us with data,” McNoldy said. “We are bound to catch more ‘marginal’ storms now than decades ago.”

This greater storm detection can explain some of the increase in the number of names, especially the short-lived, weak storms that do not impact land. The tropical Atlantic has been home to many of these so-called “shorties” this year.

Named storm count can still be a useful metric, though, as long as such nuances are considered, McNoldy said. And it is important to note that the abundance of shorties could well have roots in human-caused climate change, too.

“A warmer ocean could mean that what would have been unfavorable for storm development decades ago could now be marginally favorable, so we start seeing these systems sneak in where they were absent before,” McNoldy said.

Jacob Feuerstein is a college junior studying meteorology at Cornell University.